MR imaging of hyaline cartilage at 0.5 T: a quantitative and qualitative in vitro evaluation of three types of sequences.

Abstract

To identify an optimal pulse sequence for in vitro imaging of hyaline cartilage at 0.5 T. Twelve holes of varying diameter and depth were drilled in the cartilage of two pig knees. These were submerged in saline and scanned with a 0.5-T MR system. Sixteen T1-weighted gradient echo (GE), two T2-weighted GE, and 16 fast spin echo sequences were used, by varying repetition time (TR), echo time (TE), flip angle (FA), echo train length, profile order, and by use of fat saturation. Contrast-to-noise ratios (CNR) of cartilage versus saline solution and cartilage versus subchondral bone were measured. Cartilaginous lesions were evaluated separately by three independent observers. Interobserver variability and correlation between the quantitative and qualitative analyses were calculated. The mean CNRs of two specimens of cartilage versus saline solution ranged from 6.3 (+/- 2.1) to 27.7 (+/- 2.5), and those of cartilage versus subchondral bone from 0.3 (+/- 0.2) to 22.5 (+/- 1.4). The highest CNR was obtained with a T1-weighted spoiled 3D-GE technique (TR 65 ms, TE 11.5 ms, FA 45 degrees). The number of lesions observed per sequence varied from 35 to 69. Observer agreement was fair to good. The T1-weighted spoiled GE sequences with a TR of 65 ms, TE of 11.5 ms and FA of 30 degrees and 45 degrees were significantly superior to the other 34 sequences in the qualitative analysis. T1-weighted spoiled 3D-GE sequences with a TR of 65 ms, a TE of 11.5 ms, and a FA of 30-45 degrees were found to be optimal for in vitro imaging of cartilage at 0.5T.